I made a mistake purchasing a subscription

See the following Apple articles:

If you want to cancel a subscription from Apple

If you want to cancel a subscription from Apple - Apple Support

If the subscription that you want to cancel is not listed

If you want to cancel a subscription from Apple - Apple Support

Request a refund for apps or content that you bought from Apple

Request a refund for apps or content that you bought from Apple - Apple Support

Hello ~ Take a look here:

Subscriptions and Billing - Official Apple Support

~Katana-San~